We are working on an early 944 and a 1987 924S to service the air conditioning systems. While the problems are different, the tasks involved were similar, involving changing the expansion valve. We already documented the problems that we found with the compressor replacement on the early 944, but note that the 924S uses the later model (Series II) compressor, so it is generally available for replacement. Again we leaned on Mike Perry at MCP AC in nearby Edgewater for parts and guidance.
If you have never done it before, replacing the expansion valve involves removing the “box” from under the dash on the passenger side. This could be a daunting task that looks to be pretty tough – and scary. However, it isn’t that bad. The expansion valve is located in the back of the box next to the firewall and inboard from the AC blower fan. You just can’t get to it to replace it without taking out the box.
We will assume that you have removed the trim panel on the lower passenger side of the dash, the glove box door and the glove box.
Have the freon professionally recovered before you begin to work on it. Even if you think that the system is empty, have it done.
You start to remove the box by taking out the four bolts on the rearward side (facing the passenger compartment.) These are 10mm socket bolts. The firewall side has a mounting “bump” that fits in a square mounting flange in the firewall. Once the four bolts are out, the whole box is loose and ready to be removed.
There are two lines in the front of the box that you must separate, and they take large wrenches. Your standard wrenches up to 19mm will suffice, but the large fitting will need a 22mm wrench. There isn’t a lot of room for an adjustable wrench, but with patience you can use one if you don’t have a 22mm. Disconnect both of these lines. Also disconnect the vacuum lines, and it helps to put a piece of tape on the ends so that they don’t get lost under the dash.
Also reach under the box and disconnect the drain tube from the bottom of the box. If you don’t disconnect it, you may break the fitting that is molded into the box and have to either replace the bottom housing or come up with a replacement. You don’t want to get into that fix.
There are a bunch of electrical connectors that need to be unplugged. Some are similar and easy to mix up when reassembling, so here is a top tip – take a sharpie and number the connectors so that when you go to reassemble, #1 matches #1, #2 matches #2 and so on. You can use tape labels if that works better for you.
With the connectors disconnected, you can pull the box back. But there are two connectors that you cannot get to until you start to remove the box – the one on the fan and the the one next to the fan that plugs into the fan speed resistor. Unplug those and the box will be out in your hands and onto the bench.
The box is actually two halves. They are held together by a bunch of spring clips and three screws. Separate the bottom from the top – the top is where all the “stuff” is mounted. Put the bottom part aside.
The evaporator is now visible in front of you. The expansion valve is wrapped in foam and tape insulation. The fittings on it unscrew from the evaporator and can be loosened from the assembly with a pipe connected to it along with a brass capillary tube. There are two different expansion valves – one has a single capillary tube, and the other has a second capillary tube with a fitting on the end. Note that the curled up end to the tube is strapped to one of the pipes on the evaporator with a metal strap and some gooey insulating tape.
In our Series I 944, we found an expansion valve with the single tube. On the 924S, we also found the single tube valve. However, when we looked up a replacement, both cars call for the two tube valve – but there is no where to hook up the second tube. The listings are just wrong.
The came our second surprise. The part of the valve that screws together into evaporator is a standard #6 fitting. However, the pipe that then goes around the box and connects to the car is a metric fitting – not a standard AC #6! You can source a replacement from Porsche (PN 94457320100) for just under $200, while an “industry replacement” is less than $25. (Griffiths has it for $91) But there is another problem.
The “industry replacement” does not have the metric fitting, but instead a standard AC size fitting, so the pipe will not fit it. The “other end” of the pipe is a standard size – the only glitch is the one metric fitting.
So Mike Perry solved the problem by making up a new pipe from AC hose to replace the stock hose. It all fit together perfectly. We reinstalled the box, connected everything up with new o-rings, and charged the system.
The moral of the story is that you need to be ready to make adjustments as you go along. The part listings for the early car we worked on and the 924S were just wrong – but we were able to make changes on the fly and make it happen.
Thanks to Mike Perry at MCP for all the help!